Change project structure to a Maven Java project + Refactor (#2816)

src/main/java/com/thealgorithms/strings/Palindrome.java

@@ -0,0 +1,71 @@
+package com.thealgorithms.strings;
+
+/**
+ * Wikipedia: https://en.wikipedia.org/wiki/Palindrome
+ */
+class Palindrome {
+
+    /**
+     * Driver Code
+     */
+    public static void main(String[] args) {
+        String[] palindromes = {null, "", "aba", "123321"};
+        for (String s : palindromes) {
+            assert isPalindrome(s) && isPalindromeRecursion(s) && isPalindrome1(s);
+        }
+
+        String[] notPalindromes = {"abb", "abc", "abc123"};
+        for (String s : notPalindromes) {
+            assert !isPalindrome(s) && !isPalindromeRecursion(s) && !isPalindrome1(s);
+        }
+    }
+
+    /**
+     * Check if a string is palindrome string or not
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise
+     * {@code false}
+     */
+    public static boolean isPalindrome(String s) {
+        return (s == null || s.length() <= 1) || s.equals(new StringBuilder(s).reverse().toString());
+    }
+
+    /**
+     * Check if a string is palindrome string or not using recursion
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise
+     * {@code false}
+     */
+    public static boolean isPalindromeRecursion(String s) {
+        if (s == null || s.length() <= 1) {
+            return true;
+        }
+
+        if (s.charAt(0) != s.charAt(s.length() - 1)) {
+            return false;
+        }
+
+        return isPalindrome(s.substring(1, s.length() - 1));
+    }
+
+    /**
+     * Check if a string is palindrome string or not another way
+     *
+     * @param s a string to check
+     * @return {@code true} if given string is palindrome, otherwise
+     * {@code false}
+     */
+    public static boolean isPalindrome1(String s) {
+        if (s == null || s.length() <= 1) {
+            return true;
+        }
+        for (int i = 0, j = s.length() - 1; i < j; ++i, --j) {
+            if (s.charAt(i) != s.charAt(j)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}